1. Field of the Invention
The present invention relates to a camera configured to detect a defocus amount, a photographic lens mountable on the camera, and a camera system.
2. Description of the Related Art
Conventionally, in a camera system, such as an interchangeable lens type single-lens reflex camera, an automatic exposure (hereinafter referred to as AE) device has widely been known. The AE device photo-electrically converts an object image from a photographic lens to determine an exposure amount (exposure value).
Further, a technique of automatic focus adjustment (hereinafter also referred to as AF) has been known. The AF technique forms images of fluxes of light from an object passing through different exit pupil areas of a photographic lens on a pair of line sensors to determine the amount of deviation of the images. The amount of deviation of the images is a relative position displacement amount of a pair of image signals obtained by photo-electrically converting an object image. Then, the AF technique detects a defocus amount of the photographic lens with respect to the object based on the amount of deviation of images. Then, the AF technique drives the photographic lens based on the detected defocus amount. Further, the AF technique can include a servo mode that causes lens driving to track not only a still object but also a moving object, and can allow continuous shooting.
In a single-lens reflex camera, a factor that determines a speed of the continuous shooting includes a time period required for AE and AF and a time period required for a series of photographing operations (hereinafter referred to as a release sequence) from retraction of a mirror and driving of shutter to return of the mirror on the camera (main body) side. On the interchangeable lens side, the factor includes a time period required for a diaphragm driving sequence from reducing an aperture of a diaphragm to provide a predetermined exposure to opening the diaphragm up to a full-aperture position after completion of exposure.
Further, in a camera system, such as a single-lens reflex camera, a technique in which a camera obtains a time period required for driving a diaphragm of an interchangeable photographic lens is discussed in Japanese Patent Application Laid-Open No. 10-260449. According to Japanese Patent Application Laid-Open No. 10-260449, the technique is effective at enabling quick control of a camera system since a lens, which can communicate with a camera during driving of a diaphragm of the lens, can transmit a time period required for driving the diaphragm to the camera. However, Japanese Patent Application Laid-Open No. 10-260449 does not discuss more specific examples.
In order to enhance a continuous shooting performance, the camera system generally executes the release sequence on the camera side and the diaphragm driving sequence on the interchangeable photographic lens side in parallel. However, a conventional camera system causes a standby time on the camera side when an aperture reducing time on the photographic lens side is longer than a release sequence time on the camera side. This is remarkable during continuous shooting. This may reduce a speed of continuous shooting.